The present invention relates to technology for fabricating a semiconductor device, and more particularly, to an electrostatic discharge protection device for protecting internal circuits from static electricity and a method for fabricating the same.
If a semiconductor integrated circuit (IC) is touched by a human body or a machine that is charged with electricity, static electricity charged in the human body or the machine is discharged to the inside of the semiconductor IC through external pins and pads of the IC, and thus internal circuits of the IC are seriously damaged by an excessive current having great energy. On the other hand, the internal circuits of the IC may be damaged as static electricity charged in the IC flows out through the human body or the machine when there is contact with the human body or the machine.
Therefore, most semiconductor integrated circuits include an electrostatic discharge protection device between a pad and an internal circuit as shown in FIG. 1 to protect major circuits from the damage due to the static electricity. In general, the electrostatic discharge protection device uses a transistor.
FIG. 2A illustrates a plane view of a conventional electrostatic discharge protection device. FIGS. 2B and 2C illustrate cross-sectional views taken along an X-X′ line described in FIG. 2A in accordance with first and second prior arts, respectively. FIG. 3 illustrates a graph comparing leakage current properties of the electrostatic discharge protection devices in accordance with the first and second prior arts.
Referring to FIG. 2A, the conventional electrostatic discharge protection device includes an active region 11 defined by an isolation layer 12, a gate electrode 13 simultaneously crossing both of the active region 11 and the isolation layer 12, a junction region 16 formed in the active region 11 at both sides of the gate electrode 13, a first wire 14 connected to a pad unit and the junction region 16 at one side of the gate electrode 13, and a second wire 15 connected to a ground unit and the junction region 16 at the other side of the gate electrode 13.
However, as described in FIG. 2B, the electrostatic discharge protection device in accordance with the first prior art has a problem in that a contact area between the active region 11 and the junction region 16 is reduced and thus an electrostatic discharge protection property thereof is deteriorated as a degree of integration of a semiconductor device is increased.
As illustrated in FIG. 2C, the electrostatic discharge protection device in accordance with the second prior art that is introduced to solve the above problem includes the junction region 16 that is formed of a first junction part 16A and a second junction part 16B having a depth greater than that of the first junction part 16A in a direction where the gate electrode 13 is extended, i.e., an X-X′ direction. Like this, the contact area between the active region 11 and the junction region 16 is increased by forming the junction region 16 to include the first and second junction parts 16A and 16B having different depths from each other, so that it is possible to improve the electrostatic discharge protection property.
However, since the junction region 16 is generally formed through an impurity ion implantation process, in the second prior art, impurities are piled up on a sidewall of the isolation layer 12 close to the junction region 16 in a process of forming the first and second junction parts 16A and 16B. Further, the piled-up impurities act as a source or path of a leakage current. Referring to FIG. 5B, the leakage current of the electrostatic discharge protection device is rapidly increased compared with the first prior art. In particular, as shown in FIG. 3, an amount of the leakage current generated in a state that a constant voltage, i.e., 2 V, is supplied to the junction region 16 is 2.99 nA in the first prior art and 22.7 nA in the second prior art. That is, it is noticed that the amount of the leakage current in the second prior art is sharply increased compared with that in the first prior art.